1. Field of the Invention
This invention relates to a method for preparing 2-pyrazolin-5-ones. More particularly, this invention concerns a method for preparing 1-aryl-3-arylamino-2-pyrazolin-5-ones from N-aryl-3-arylamino-3-oximinopropionamides. In one aspect this invention relates to a process for preparing 1-aryl-3-arylamino-2-pyrazolin-5-ones that are particularly useful as color-forming couplers or as intermediates in preparing color-forming couplers which produce dyes in photographic elements.
2. Description Relative to the Prior Art
It is well known in the photographic art to form colored photographic images by means of a coupling reaction between an oxidized primary aromatic amine developing agent and a color-forming coupler. In such processes 2-pyrazolin-5-ones are known to be useful as couplers for forming magenta dyes. Many references describe such use of 2-pyrazolin-5-ones and also describe methods for synthesizing the compounds. See, for example, U.S. Pat. Nos. 4,113,954; 3,798,234; 3,615,506; 3,419,391; 3,062,653; 2,865,748; 2,600,788; and 2,343,703; British Pat. Nos. 1,134,329; 1,129,334; and 1,129,333; and Canadian Pat. No. 817,887, all of which are hereby incorporated herein by reference. Copending U.S. patent application Ser. No. 220,409, filed December 29, 1980, now U.S. Pat. No. 4,345,085 describes a method for preparing 2-pyrazolin-5-ones from 1,2,4-oxadiazoles.
Among the 2-pyrazolin-5-ones, the 1-aryl-3-arylamino-2-pyrazolin-5-ones are particularly useful as couplers or as intermediates in preparing couplers. It is always desirable to have new synthetic routes to such pyrazolones, especially new syntheses which are more efficient and economical than other known methods. The present invention provides such a synthetic route to 1-aryl-3-arylamino-2-pyrazolin-5-ones. The new synthesis involves dehydrative cyclization and rearrangement of N-aryl-3-arylamino-3-(O-acyloximino)propionamides and is not described or suggested in any of the references cited above.